March 18, 2009

It is suggested that some pea aphids, a crop pest, are tolerant to heat stress because of bacterial symbionts, Buchnera aphidicola. Members of a strain of heat-sensitive pea aphids with only a non-resistant symbiont were put in 2x2x2m mesh cages, and heat shocks were simulated by putting plastic sheets over the cages (increasing temperature by ~5°C to what would normally affect pea aphid reproduction but still occur naturally). Introduction of predators does not necessarily cause the number of aphids to drop. The number of pea aphids was reduced when subjected to heat shocks, and the presence of 7-spot ladybird predators made no difference (X2 = 2.4, P > 0.5). However, when harlequin ladybirds were introduced, the effect of heat shock was alleviated (X2 = 41.8, P <10–6) because they only predate when population density of aphids is high.